Figure A.1.3.2.1-1 shows a call flow for blind transfer when IMS serving the transferor provides data channel service.
Step 1.
UE-A calls UE-B, UE-A sends an INVITE request towards the UE-B.
Step 2.
DC media resource is allocated by IMS-B for UE-A and UE-B.
Step 3-6.
UE-B answers the call, session connection is established between UE-A and UE-B. IMS-B establishes BDC connection for UE-A and UE-B. And then IMS-B establishes ADC connections between UE-A and UE-B.
Step 7.
UE-B starts transfer process.
Step 8.
UE-B sends a REFER message to transfer the call to UE-C.
Step 9-10.
IMS-B sends 202/NOTIFY to UE-B to accept the transfer request, and then sends BYE message to UE-B.
Step 11.
IMS-B releases all the allocated data channel media resources on MF for UE-A, UE-B.
Step 12-17.
IMS-B sends an INVITE message to UE-C, the audio along with data channel media connections are established between UE-A and UE-C, the data channel media can be provided either by IMS-A or IMS-C or both.
Figure A.1.3.2.2-1 shows a call flow for consultative transfer when IMS serving the transferor provides data channel service.
Step 1.
UE-A calls UE-B, UE-A sends an INVITE request towards the UE-B.
Step 2.
DC media resource is allocated by IMS-B for UE-A and UE-B.
Step 3-6.
UE-B answers the call, session connection is established between UE-A and UE-B. IMS-B establishes BDC connection for UE-A and UE-B. And then IMS-B establishes ADC connections between UE-A and UE-B.
Step 7-8.
UE-B holds UE-A, and then calls UE-C.
Step 9.
When UE-C sends 180 ringing or 200 response, UE-B starts transfer process.
Step 10.
UE-B sends a REFER message to transfer the call to UE-C.
Step 11-12.
IMS-B sends 202/NOTIFY to UE-B to accept the transfer request, and then sends BYE message to UE-B.
Step 13.
IMS-B releases all the allocated data channel media resources on MF for UE-A, UE-B and UE-C.
Step 14-18.
IMS-B sends a media re-negotiation request with to establish the connection between UE-A and UE-C.
Step 19.
The audio along with data channel media connections are established between UE-A and UE-C, the data channel media can be provided either by IMS-A or IMS-C or both.